Figure 4.

Ensemble Achilles tendon stress patterns at the five walking speeds. Peak stress and both medial gastrocnemius and soleus activity progressively increase with walking speed. Late swing Achilles tendon loading arises without discernable plantarflexor muscle activity. However, gastrocnemius elongation (ΔL, relative to upright length) in late swing aligns temporally with tendon loading, suggesting the loading is induced by passive stretch. Simultaneous tibialis anterior muscle activity counters the ankle torque induced by the Achilles tendon.